1. Field of the Invention
This invention relates to attitude control systems for spacecraft and, more particularly, to such control systems which can be self-contained on a satellite in geosynchronous or other type of orbit.
2. Description of the Prior Art
In systems employing geostationary spinning satellites, as perhaps with certain other earth satellite systems, it becomes necessary from time to time to determine the spin axis attitude and to execute attitude trim maneuvers. These maneuvers are needed in order to compensate for the spin axis precession which is caused by solar torque.
In predecessor systems, such attitude trim maneuvers have been commanded from ground control stations. In such systems, data which was pertinent to the determination of satellite spin axis attitude was collected by onboard sensors and telemetered to the controlling ground station. There the data was processed to determine the appropriate attitude trim corrections. These were then transmitted to the satellite as command signals to perform the necessary attitude trim maneuvers. This performance of attitude trim correction in real time under ground control requires an operator in the control loop, is subject to anomalies from operator error, transmitted signal interference and the like, and imposes an operational burden on ground control systems. It would be desirable, therefore, to have the required attitude trim maneuvers determined and controlled by systems which are entirely self-contained on the satellite.